The background to the invention will be explained in relation to a particular application. Other applications may occur to the reader.
In a conventional digital telecommunications network, each network element generally has a facility to report the error rate in the paths which utilise it. The reported error rate is based on the total detected errors from the beginning of the path to the network element. The error rate is reported in the SDH (synchronous digital hierarchy) or SONET (Synchronous Optical NETwork) overhead. This information is useful, for example, in maintaining a quality of service which may be assigned to any particular path. A problem arises when the path crosses the boundary between one operator domain and another. If the error rate reported at the receiving users end is undesirably high, how can the operator responsible be identified?
A solution has been proposed to the problem and is called TCM (“tandem connection monitoring”). As proposed, each network element at a potential domain boundary would have additional facilities to report tandem connection error rate in the SDH or SONET overhead. As a path enters a domain, the error rate would be reset to zero so that as the path leaves the domain the tandem connection error rate would represent the errors occurring only within that domain. Unfortunately, because the facility is required in addition to the “normal” error reporting, and because each network element may form part of many paths (for more complex elements potentially tens of thousands), the cost implications for each network element where TCM support is required, in terms of application specific integrated circuits (ASICs) and software, are so great that few network elements are offered with the facility. In addition, many elements which do provide the facility, can only support the facility for a subset of the paths passing through that element.